The Sims 2: Bon Voyage is my first expansion pack, and I would say it's very good, but sometimes it can take forever to load, especially when my sims are buying souveniers and walking home. Basically, you can create holiday destinations for a particular town-like making a downtown-and it can be one of 3 themes: woodland, tropical island or eastern. You can make holiday cottages for your sims, then they can buy them and stay in them from 3-6 days (you choose when you're booking your holiday on the phone beforehand). They can also stay in hotels and inns.
Some of it is a bit complicated; the installing is confusing and I had to work out for myself that I had to use the Bon Voyage disk to play, not my Double Deluxe disk, which is weird. Also, your sims want lots of different things once the game is installed, for example my family on holiday wanted to find bigfoot and wasted their holiday looking for him in all of the community lots.
Once the expansion pack is installed, lots of new furniture and clothes are evailable, so there are kimonos, shorts, grass skirts, new four-poster beds and circular tables, which are very useful for hotels.
Having Bon Voyage installed (and having to use the disk during gameplay) makes it no different from before, except that there are different options when you click on the people (they can take pictures of each other and walk places instead of taking the car) and there is a new button on the toolbar at the top.
I think that the best things on Bon Voyage are the music, clothes and the different destinations. I haven't made an eastern one yet but the tropical island destination is definitely the best, I don't know why.
There are also a lot of new hairstyles and and your Sims can buy jewellery at the shops, but I won't give away too much!